1. Field of the Invention
The present invention relates to a lifter for adjustably raising or lowering a seat of automobile, and is particularly directed to a drive and operation mechanism of the lifter.
2. Description of the Prior Art
A variety of lifters have been invented and used for automotive seats, and most of them are actuated by rotation of an operation lever to raise and lower the seat cushion of the seat. For example, known is the lifter disclosed in the Japanese Laid-Open Patent Publication No. 57-37030. This prior art is of such construction that, when in use, the operation lever is drawn out of a housing for increasing its length and then vertically rotated for causing the vertical displacement of the seat cushion. Therefore, the lifter operation is effected easily by applying a small force upon such extended operation lever. According to the prior art, however, the housing and operation lever are formed in a mutually integral reation, and in particular, the housing is directly connected to a drive shaft in spline connecting manner, the drive shaft being adapted for imparting a rotational force applied on the operation lever to a drive mechanism so as to adjustably move the seat frame in a vertical direction. Consequently, for raising the seat to the highest level, the operation lever needs to be rotated at over 45 degrees, or rather, as the case may be, it needs to be rotated at over 180 degrees, and an undesired, abnormal rotational angle is required for the operation lever. In that case, further, since the operation lever is disposed at the lateral side of the seat cushion and adjacent to the floor of automobile, the rotation range of the lever is limited within at most 180 degrees and thus can never be rotated around at 360 degrees.
In general, an ideal rotation range of the operation lever for this kind of lifter is approx. 45 degrees above and below a non-use horizontal position of the lever, which is a most comfortable design for operation of lever at the side of an occupant on the seat, who is to operate the lever with his or her seating posture.
Certainly, the prior art suggests the extendability of the operation lever and the provision of springs for helping to give a drive force towards the link members, in order to reduce the operation force required to rotate the drive shaft and associated mechanisms. But, the structure results in a rather complicated mechanism and the undesired rotation range problem associated with the operation lever remains.